The Consumer Federation of America, an alliance of advocacy groups, wants to raise the standard well above the hike the government is proposing. The government's proposal would require automakers' fleets of cars to average 35.7 miles per gallon by 2015. Light trucks would have to average 28.6 miles per gallon.

The National Highway Traffic Safety Administration offered those standards in April, and the public had until Tuesday to comment. The agency will issue a final rule after reviewing the public's reaction, but the date is undetermined.

This will be the first time that the agency has increased its so-called Corporate Average Fuel Economy standards for passenger cars since 1985.

Congress passed and President Bush approved in December a requirement that the agency set "maximum feasible" yearly mileage levels that would lead to a minimum standard of 35 miles per gallon by 2020. This figure averages passenger cars and light trucks. The law also gave the agency the authority to go higher than that standard.

Charles Territo, a spokesman for the Alliance of Automobile Manufacturers, a Washington-based trade association that represents 10 major auto companies, said the agency's mileage standards weren't feasible or cost effective in such a short time.

Automakers could reach the government's 2020 target, he said. But the highway agency is demanding that they start making big mileage gains in 2011, Territo said, and that's "too aggressive."

It's hard to be too aggressive, countered Jack Gillis, the director of public affairs for the Consumer Federation of America, given $4 a gallon gas.

"Americans were crying out for help, and Congress provided a blueprint for assistance," Gillis said in a conference call Tuesday. "Sadly, they (the National Highway Traffic Safety Administration) have failed."

Gillis' group and Public Citizen, another Washington consumer organization, noted that the agency's mileage standard assumed a gas price of $2.42 per gallon in 2016.

"The recent dramatic increases in gas prices makes it imperative that NHTSA reconsider its cost-benefit models and propose the maximum, feasible fuel standard," the group said in a statement.

The Consumer Federation of America proposes 39.5 miles per gallon for passenger cars and 30.9 miles per gallon for light trucks by 2015.

Territo responded: "The high price of gas will increase the popularity of more fuel-efficient vehicles, but it doesn't decrease the cost or the amount of time necessary to develop these types of vehicles."